Essays for Midterm 2
On the second midterm exam, you were asked to write an essay
on one of the following two topics:
1. The eye is a complicated feature of the human body. How
does it work? Discuss the relevant
physics. In your essay, include
answers to the following questions: what does it mean to be nearsighted or
farsighted? How does aging play into this process? How does the eye see colors?
What does it mean to be colorblind?
For
an essay that earned the full 20 points, see the one by Derek Chen.
OR
2. Greenhouse effect. Explain how it works, and how it
affects climate. How is it affected by human emissions? Why is the greenhouse effect
"controversial" in public debate? How does it relate to the "ozone problem"?
For
an essay that earned the full 20 points, see the one by Stephanie
Ho.
The eye works by having light focus on your retina through
the help of two lenses, the cornea and the lens. The brain then interprets the signal and makes an
image. To be nearsighted means to
have the light focus too quickly because the cornea is too curved. (This can be solved with a concave lens
such as contacts or glasses). To
be farsighted means to have light focus beyond the retina. This problem is solved with a convex
lens. Aging plays into the process
of sight because as you grow older your lens loses its flexibility and there is
a loss of accommodation. You
cannot see things close up because you're farsighted.
The eye senses brightness with rods and color with
cones. Cones can only sense the
colors red, blue, and green so it can be fooled into thinking a computer screen
is white when the screen is actually made up of tiny red, blue, and green
lights. Colors other than RBG are
sensed by measuring the intensity of each color received and having the brain
that message. To be colorblind
means to not be able to distinguish from red and green because one of your cone
sensors doesn't work. It does not
mean you see in black and white.
In a sense we are all colorblind because we see only three colors.
Greenhouse effect by Stephanie Ho
Contrary to popular belief, the greenhouse effect is not a
completely negative aspect. In
fact, it is this effect that keeps the Earth at a temperature hospitable to
human life. How the greenhouse
effect works is that sunlight enters the Earth's atmosphere, where it is
absorbed by the Earth's surface (which is heated up). The Earth's surface then emits light in the form of infrared
waves. However, not all of the IR waves
are able to escape the Earth's atmosphere, as roughly half of it is trapped by
the molecules in the air.
The infrared waves can be absorbed by carbon dioxide, O3,
and water vapor, among other molecules.
As the average temperature of the Earth's surface has increased 1C over
the past few years, environmentalists and the media have portrayed this problem
to be a direct consequence of human activity. Increased burning of fossil fuels have released an
increasing amount of carbon dioxide, a molecule known to further trap IR. Evidence that human activity can substantially
affect the environment has been found in "the ozone problem." Human usage of Freon (a
chloroflorocarbon) has already been proven to break up the molecules of the
ozone into O and O2. An "ozone
hole" has already been found over Antarctica, where nitric acid crystals
that form in spring enhance the problem.
However, the greenhouse effect is controversial because
studies have shown that even with the noted increase of CO2, the temperature of
the Earth should have increased by only 0.1-0.2C, rather than the observed 1C. Some like to say that the Earth has
experienced temperature changes in the past and that the increase is natural
while others still argue that even this excess can be caused by second-hand
effects of CO2 resulting in water vapor.
In the end, correlations cannot definitely prove cause and effect and
there is no way to tell for sure if humans are directly responsible for the
increased greenhouse effect. It
comes down to whether the risk that it is is worth gambling.